This invention is related to sensors applied to the body for monitoring or making measurements of body tissue condition, metabolism or other body functions indicative of health. More specifically, the invention is directed to an appliance which can be readily attached to the body to support a sensor adjacent thereto in a stable disposition for accurate and precise measurements unhampered by artifact due to sensor motion relative to the body.
One application for a probe system of the type described herein is in pulse oximetry, a non-invasive method of measuring the relative oxygen saturation of the blood. Pulse oximeters generally employ light sources, e.g., light emitting diodes (LEDs), to alternately direct light of two different wave lengths, e.g., red and infra-red, to the blood through the skin. The light transmitted or reflected by the blood at the different wave lengths can then be compared to provide a measurement of oxygen saturation.
Typically, a probe system containing the light sources, e.g., LEDs, and a light sensor, e.g., photodetector, is mounted on an appendage of the body, e.g., the finger, toe, ear lobe, nose, hand or foot, although it can be used on virtually any cross section of tissue having pulsatile blood flow which can be penetrated by light emissions from the light source. An example of such a sensor is disclosed in U.S. Pat. No. 4,830,014 to Goodman for Sensor Having Cutaneous Conformance. In the probe system of the aforementioned Goodman patent, the light source and sensor are embedded within a flexible adhesive substrate used for attachment to the appendage. With repeated applications, the adhesive progressively loses its tack. Hence, the adhesive substrate must be frequently disposed of due to loss of adhesive tack as well as for infection control. Because the sensor elements are embedded within the substrate, they too are discarded.
Because the sensor elements account for the most expensive part of the probe system, it is desirable to be able to reuse them and only dispose of the positioning substrate. Until the instant invention, the use of sensor elements separable from a flexible substrate in which the required stability could be achieved in use was unknown.